The invention relates to an opening-closing mechanism for opening and closing a door member with respect to a box-shape base member, and also relates to an opening-closing device using the same. Incidentally, in the specification, the “box-shape base member” widely includes various storage base portions and housings, and the “door member” widely includes a covering member, a shielding member and the like.
FIGS. 8(a), 8(b) and 9(a), 9(b) show two conventional opening-closing mechanisms of a door member, which belong to a type where the door member is rotated to shift among various opening-closing mechanisms of the door members. The opening-closing mechanism shown in FIG. 8(a) has a mechanism similar to, for example, the one disclosed in Japanese Patent Publication (TOKKAI) No. 09-20177. In the mechanism, a door member 42 is rotated by substantially 90 degree with respect to an opening portion of a box-shape base member 41 to be opened and closed. More specifically, a damper device 43 having a rotary gear 43a is disposed on a sidewall portion of the base member 41. The door member 42 includes arm portions 44 projecting from both sides thereof, and circular arc shape gears 44a provided to the arm portions 44 to engage the rotary gears 43a, so that the door member 42 is rotatably connected to the sidewall portion of the base member 41 through a pivot shaft 45, and is locked at a closed position shown by solid lines by a locking device, not shown. An urging spring 46 is provided between the arm portion 44 and the base member 41 so that the door member 42 is always urged toward an open position shown by a phantom line. In the mechanism, when the locking device is released through a pushing operation of the door member 42, the door member 42 is rotated toward the open position by the urging spring 46. When the door member 42 is rotated against the urging force of the urging spring 46, the door member 42 is held at the closed position by the locking device. The damper device 43 damps a rotating speed of the base member 41 through engagement between the rotary gear 43a and gear 44a. 
Also, in an opening-closing mechanism as shown in FIGS. 9(a), 9(b), a door member 52 is rotated by substantially 90 degree with respect to an opening portion of a box-shape base member 51 to shift the door member 52 from a closed position shown in FIG. 9(a) to an open position (one dot chain line in FIG. 9(b)). The mechanism includes shafts 54a, 54b projecting from each arm portion; a guiding groove 56 provided to each sidewall portion 55 of the base member to be engaged with the shafts 54a, 54b; an urging spring 53 for urging the door member 52 toward the open position; and a locking device (not shown) for holding the door member 52 at the closed position. The guide groove 56 has a branch groove 56a on one side thereof. The branch groove 56a allows the shaft 54a to enter therein at a side slightly before a position Where the door member 52 is disposed at the closed position when the door member 52 is going to rotate around the shaft 54b as a supporting shaft. With this entering, the door member 52 makes its final rotation to be disposed on the final closed position. One end of the urging spring 53 is engaged with an engaging portion 57 at a side of the base member 51, and the other end thereof is engaged with the shaft 54a to provide a tensile force between the engaging portion 57 and the shaft 54a. The base member 51 includes a damper device 58 with a rotating shaft 58a incorporated into a sidewall portion 55. One end of an arm 59 is integrally and rotatably connected to the rotating shaft 58a. The other end of the arm 59 is linked to the shaft 54b. 
In this mechanism, it is configured that the door member 52 is automatically opened by the urging spring 53 as much as possible when the locking device of the door member 52 in the closed position is released, as described in the following steps. At the beginning of the opening operation, the door member 52 is rotated in a direction toward the open position by the urging pressure of the urging spring 53 after the shaft 54a slips out of the branch groove 56a with the shaft 54b as a supporting point and is returned to the guiding groove 56 as shown in FIG. 9(b). In other words, the door member 52 is rotated around the shaft 54a within a section a shown in FIG. 9(a) where the shaft 54b does not move and only the shaft 54a moves. Then, the door member 52 is moved at a damped speed according to the rotation of the arm 59 of the damper device 58, and the opening portion of the base member 51 is fully opened, i.e. the door member 52 is shifted to the open position, when the shaft 54a reaches the terminal.
The opening-closing mechanism as shown in FIG. 8(a) is of a mono-axial type where the door member 42 is rotated around the pivot shaft 45 as a supporting point. Its operation is characterized such that the door member 42 projects upward higher than the base member 41 in a state that the door member 42 is shifted to the open position as shown by phantom lines, thereby enlarging a length h1 in FIG. 8(a). Therefore, as the opening-closing device, for example, when an article is put into or taken out of the base member 41, the article easily hits the projected portion of the door member 42, and its appearance also becomes poor. Incidentally, the problem can be solved by reduction of the length hi to a length h2, as shown in FIG. 8(b), by enlarging the arm portion 44 so that the pivot shaft 45 as a supporting point is lowered. However, in this case, the door member 42, shown by the phantom lines, disposed on the open position is greatly separated from the base member 41. At this time, a length t as shown in FIG. 8(b), i.e. a space when the door member 42 is disposed on the opened position, is required to be large. For example, there is a problem in a case that the base member 41 is to be disposed in a concave as an installation place, or in a case that the door member 42 is to be disposed inside the base member 41 and the door member 42 is placed at the opened position.
The opening-closing mechanism as shown in FIGS. 9(a), 9(b) has been developed in order to solve the above-described problems. However, the mechanism has problems from the following points of view. In the mechanism, the shafts 54a, 54b are made of metal for its rigidity and operational points. Moreover, the pair of the shafts 54a, 54b is provided on each side, thereby requiring total four shafts, resulting in poor assembling ability and a higher cost. From an operational point of view, while the shaft 54a is moving in the section a and the door member 52 is rotated in the direction of the open position, the damper device 58 does not act on the door member 52. The damping does not work effectively until the door member 52 is rotated as the shaft 54a is moving in a section b. Therefore, the door member 52 is rotated too quickly or slowly in the section a at the beginning in the direction of the open position, and is gently rotated in the section b by being damped as designed, so that the speed is changed stepwise and a continuous smooth movement can not be obtained.
In view of the above defects, the present invention has been made, and an object of the invention is to provide an opening-closing mechanism and an opening-closing device that solve all of the above problems. Specifically, when compared with the conventional mechanism as shown in FIGS. 8(a) and 8(b), the portion of the door member projected upward from the base member at the opened position is made smaller, and the door member is damped through an engagement of various gears. When compared with the conventional mechanism as shown in FIGS. 9(a) and 9(b), the operational characteristics and assembling ability can be improved.
Further objects and advantages of the invention will be apparent from the following description of the invention.